WiMAX, short for worldwide interoperability for microwave access, is currently defined by the Institute of Electrical and Electronics Engineers, or IEEE, 802.16-series specification. Mobile WiMAX, under 802.16e, permits broadband wireless access for mobile users, while 802.16m is the advanced air interface standard. Base stations and mobile stations may support 802.16e only standard (legacy) or mixed standards (802.16e and 802.16m).
Zone switching is a method for IEEE 802.16m-capable mobile stations to switch from a legacy 802.16e (mobile WiMAX) zone to an 802.16m (advanced air interface) zone in a mixed-mode 802.16m base station that offers legacy support. A zone switching operation enables an 802.16m mobile station to perform handover from a legacy base station to an 802.16m base station. The 802.16m mobile station first performs a 802.16e-to-802.16e handover, then performs an 802.16e-to-802.16m zone switch at the same base station. This provides flexibility for the base station to balance its load between the 802.16e zone and the 802.16m zone, without changing its 16e/16m zone ratio, which is a major configuration change that should not happen very often.
To enable zone switching, a non-trivial issue to be resolved is how to perform a security update. The advanced air interface standard (802.16m) uses a different security key hierarchy than the mobile WiMAX standard (802.16e). Furthermore, for network deployment, the access service network gateway (ASN-GW) and authenticator may be in the mixed mode as well, such that the mobile station does not have knowledge about whether its current anchor authenticator access service network (AA ASN) is 16m-capable or not, even if it is currently associated with a 16m base station in its 16e zone.
Thus, there is a continuing need for a method to ensure a security update is properly performed before an 802.16e-to-802.16m zone switch is triggered.